Composition of a conductive ceramic glaze and improved method of forming same

ABSTRACT

A composition of matter utilized by particular method for forming an electrically conductive glaze upon the outer surface of a ceramic mold form wherein the combination includes approximately 33 percent soda feldspar, approximately 20 percent flint, approximately 9 percent calcium carbonate, approximately 1 to 2 percent ball clay, approximately 2 percent kaolin, approximately 7 percent zinc oxide and approximately 27 percent black iron oxide, all percentages being taken by weight, the method including the addition of an amount of flocculant such as 20 percent magnesium sulfate solution or deflocculant such as sodium tetrapyrophosphate or sodium silicate to control the viscosity of the solution and thereby control the thickness of the layer formed upon the external surface of the ceramic mold form, including the spraying or dipping of the mold form in the resulting solution for coating thereof as well as the firing of the coated ceramic mold form in a furnace or approximately 2200 to 2300 degrees Fahrenheit for approximately a 30 hour cycle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Ceramic molds are usually used as the form about which the rubber isplaced for making high quality rubber gloves. The present composition isusable as a glaze about the external surface of such a ceramic moldwhich glaze itself is electrically conductive to facilitate themonitoring for imperfections of the gloves formed thereon. Also theconductive surface serves to increase the flow of heat to the glove tofacilitate curing thereof. Preferably the conductive glaze is of a blackcoloration to enhance thermal retention characteristics of the moldform.

In practice a glove will be formed about a ceramic mold having theconductive glaze of the present invention therearound. Prior to removalof the glove from the form, the composite unit may be dipped in anelectrolytic solution so that the conductive glaze itself will act asone electrode and another electrode may be placed in the electrolyte. Inanother method the glove need not be dipped in an electrolytic solution,but an electrode may be manually or otherwise caused to pass over thesurface of the glove and visual arcing of a surge reading on a voltageor current meter will indicate an imperfection. In either systemapplication of a voltage difference across the two electrodes will causeelectrical current to flow between the electrodes only if animperfection exists in the wall of the gloves at any point such thatelectric current may flow therethrough. However, if the glove is withoutimperfections the flow of current between the electrodes will beprevented. In this manner a glove can be tested for imperfections in aone-step process without requiring the removal of the glove from themold form or the placing of the glove in a special test apparatus.

2. Description of the Prior Art

In the prior art the primary difficulty in the forming of electricallyconductive glazes for ceramic mold forms was the lack of repetitiveconsistency of resistivity between one fired glaze and the next firedglaze. It is desirable to use a ceramic glaze having repeatablyconsistent surface resistivity. The prior art conductive glazes did nothave this quality but the improved composition of the glaze as disclosedand claimed in the present invention provides a more repetitiveconsistency in surface resistivity than possible with any prior artcompositions.

Particularly, the components of the glaze of the present invention arereasonably inexpensive as well as being very accessible.

Most prior art conductive surfaces on molds are achieved by usingelectrically conductive coatings rather than using the ceramic itself asthe conducting agent. Conductive coatings tend to wear off quickly whennot using the present invention but a conductive ceramic glaze has avery extended useful lifetime.

SUMMARY OF THE INVENTION

The present invention provides an improved composition for forming anelectrically conductive glaze on the external surface of a ceramic moldform. The main components of the glaze include approximately by weight33 percent feldspar, 20 percent flint, 9 percent calcium carbonate, 1-2percent ball clay, 2 percent kaolin, 7 percent zinc oxide and 27 percentblack iron oxide.

This overall glazing composition is added to water in an approximateratio of 5 parts of the original composition to 4 parts water, or anamount of water is added to cause the resulting solution to assume aspecific gravity of approximately 1.57 preferably, or at least withinthe range of 1.52 to 1.62.

The feldspar should be a soda feldspar and the flint should be filteredthrough a #325 mesh filter. This entire composition is then screened byan electric shaker through a #150 mesh filter followed by an amount offlocculent such as magnesium sulfate 20 percent solution for adjustingor the viscosity of the final dipping solution. The magnesium sulfatesolution is operable to allow the smooth application of the glazingformula to the external surface of the mold form. If necessary adeflocculent can also be utilized to control viscosity.

This coated mold form is now placed in a furnace for firing at a maximumtemperature of approximately 2200 to 2300 degrees for a 30 hour cycle toform a black semi-gloss electrically conductive glaze on the externalsurface of the mold. This composition and method is reproducible toconsistently provide a surface resistivity of 50,000 to 150,000 ohmswhen measured at points 1 and 2 inches apart.

It is the preferred embodiment of the present invention to provide aceramic mold form having an electrically conductive glaze about theexternal surface thereof.

It is an object of the present invention to provide an improvedelectrically conductive glaze upon the surface of a ceramic mold whichis reproducible such that the glaze has a surface resistivity of 50,000to 150,000 ohms when measured at points 1 to 2 inches apart.

It is an object of the present invention to provide an improvedelectrically conductive glazing composition which assumes a blacksemi-gloss finish after firing.

It is an object of the present invention to provide an improvedcomposition for forming an electrically conductive glaze upon theexternal surface of a ceramic mold form which composition has anadjustable viscosity controllable by the addition of an amount offlocculent or deflocculent to assure smooth flow during application ofthe glazing material upon the mold form prior to firing.

It is an object of the present invention to provide an improved solutionfor forming an improved electrically conductive glaze upon a ceramicmold wherein the thickness of the formed glaze is controlled by theadjusting of the specific gravity of the glazing solution.

It is an object of the present invention to provide an improvedelectrically conductive composition for glazing a ceramic mold formwherein the specific gravity is adjusted by controlling closely theamount of water added thereto prior to coating of the mold form.

It is an object of the present invention to provide a method for glazinga ceramic mold form including the firing of the coated mold form in aconveniently reproduceable manner to provide a consistentlyreproduceable surface resistance of the resulting conductive glaze.

It is an object of the present invention to provide an improvedcomposition and method for forming an electrically conductive glaze onthe external surface of a ceramic mold form which is usable with avariety of sizes of mold forms.

It is an object of the present invention to provide an electricallyconductive glaze upon a ceramic mold form which is capable of beingproduced for reasonably low cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention is particularly pointed out and distinctly claimedin the concluding portions herein, a preferred embodiment is set forthin this detailed description.

The purpose of the composition and method of the present invention is toprovide a composition for forming an electrically conductive glaze uponthe external surface of a ceramic mold form having a surface resistivityof approximately 50,000 to 150,000 ohms when measured at points 1 and 2inches apart and which is easily reproducible within these tolerances.The preferred embodiment set forth in this detailed description providesa total material having a weight of 20 pounds and one half ounce. Thismaterial, including soda feldspar, flint, calcium, carbonate, ball clay,kaolin, zinc oxide and black iron oxide, is added to approximately 7000ccs. of warm-to-hot water such that the specific gravity of theresulting solution is approximately 1.57. This solution is then adjustedfor viscosity by the addition of an amount of flocculent such asmagnesium sulphate 20 percent solution. Alternatively, if needed theaddition of a deflocculent such as sodium tetrapyrophosphate or soliumsolicate could be added. Then the ceramic mold itself is coated andfired in order to form the final electrically conductive glaze thereon.

Initially each of the ingredients listed below is weighed. The specificsof each of the seven components of the original material are listed inthe below table:

    ______________________________________                                                                   PER-  PERCENTAGE                                                              CENT- TOLERANCES                                   MATERIAL    LBS.   OZS.    AGE   BY WEIGHT                                    ______________________________________                                        Feldspar (Soda)                                                                           6      10      33.0  30.0-35.0                                    Flint (325 Mesh)                                                                          4      1       20.2  18.0-22.0                                    Calcium Carbonate                                                                         1      13      9.2   7.0-11.0                                     Ball Clay (English)                                                                       0      31/2    1.1   1.0-2.0                                      Kaolin      0      7       2.2   2.0-4.2                                      Zinc Oxide  1      7       7.3    5.0-10.0                                    Black Iron Oxide                                                                          5      7       27.0  25.0-30.0                                                20     1/2     100.0                                              ______________________________________                                    

Each of the seven material listed above is initially independentlyweighed. The black iron oxide is held separately and the remaining sixingredients are physically mixed. Initially the iron oxide is added toat least a portion of the 7000 ccs. of water and mixed. The mixing maybe performed by stirring on an electric mixer for approximately 10minutes or possible ball milling for up to 3 hours. The remaining sixingredients are then added and the entire composition is stirred forone-half hour. Additional water is now added to bring the specificgravity within the limitations of 1.52 to 1.62 but most preferably toapproximately 1.57. The exact amount of water finally added can varywithin the tolerances and in this manner the final thickness of thecoating of material upon the external surface of the ceramic mold iscontrolled. With a higher specific gravity the coating will be thickerwhereas with a lower specific gravity the coating will be thinner. Thisadjustment can be made with each run as desired in order to vary thethickness of the final conductive glaze.

This solution now having the desired specific gravity may be screenedthrough a #150 mesh on a shaker such as an electric shaker or the like.Then the viscosity of the solution is adjusted to assure a smoothapplication flow during dipping or spraying by the addition of an amountof magnesium sulphate 20 percent solution which acts as a flocculent.This solution is added sparingly since a few drops will change theviscosity substantially due to chemical reaction with the material.However, should deflocculent be needed then a small amount of sodiumtetrapyrophosphate or sodium silicate may be added.

The now properly dipped or sprayed, wet ceramic mold form will be placedwithin a furnace for firing. Preferably the firing will be performed inan oxidizing environment wherein the temperature is raised toapproximately 2260 degrees Fahrenheit and then down to room temperatureover a 30 hour cycle. This will result in a black semi-gloss finishbeing assumed by the electrically conductive glaze as well as a surfaceresistivity in the range of 50,000 to 150,000 ohms when measured atpoints 1 and 2 inches apart.

One of the primary advantages of the present invention is the ability toconsistently produce electrically conductive glazes having surfaceresistivity more closely held within the above-defined tolerances. Aslong as each of the materials is included within the percentage rangesclaimed and disclosed in this invention this surface resistivity will bemaintained within the described limit. Thus a consistency of resistivityin the resulting glaze is achieved by using the composition disclosedand claimed in the present invention as well as the method disclosed andclaimed herein.

While particular embodiments of this invention have been shown in thedrawings and described above, it will be apparent, that many changes maybe made in the form, arrangement and positioning of the various elementsof the combination. In consideration thereof it should be understoodthat preferred embodiments of this invention disclosed herein areintended to be illustrative only and not intended to limit the scope ofthe invention.

I claim:
 1. An improved electrically conductive composition for glazinga ceramic mold form including a first combination comprising:(a)feldspar: 30.0-35.0 percent by weight; (b) flint: 18.0-22.0 percent byweight; (c) calcium carbonate: 7.0-11.0 percent by weight: (d) ballclay: 1.0-2.0 percent by weight (e) kaolin: 2.0-4.2 percent by weight;(f) zinc oxide: 5.0-10.0 by weight (g) black iron oxide: 25.0-30.0 byweight
 2. The composition as defined in claim 1 wherein said feldspar isa soda feldspar.
 3. The composition as defined in claim 1 wherein saidflint has been filtered through a #325 mesh filter.
 4. The compositionas defined in claim 1 further including water added thereto.
 5. Thecomposition as defined in claim 4 wherein three to five parts of waterby weight is included for each five parts of said first combination. 6.The combination as defined in claim 4 wherein approximately four partsof water by weight is included for each five parts by weight of saidfirst combination.
 7. The composition as defined in claim 6 furtherincluding the addition of an amount of flocculent to achieve desiredviscosity.
 8. The composition as defined in claim 7 wherein saidflocculent is a 20% solution of magnesium sulphate.
 9. The compositionas defined in claim 6 further including the addition of an amount ofdeflocculent.
 10. The composition as defined in claim 9 wherein saiddeflocculent is sodium tetrapyrophosphate.
 11. The composition asdefined in claim 9 wherein said deflocculent is sodium silicate.
 12. Anelectrically conductive composition for glazing a ceramic mold formcomprising:(a) a first combination including:(1) soda feldspar:30.0-35.0 percent by weight; (2) flint (filtered through #325 mesh):18.0-22.0 percent by weight; (3) calcium carbonate: 7.0-11.0 percent byweight; (4) ball clay: 1.0-2.0 percent by weight: (5) kaolin: 2.0-4.2percent by weight; (6) zinc oxide: 5.0-10.0 by weight; (7) black ironoxide: 25.0-30.0 by weight; and (b) water added in an amount equal tobetween 60 and 100 percent by weight of said first combination.
 13. Thecomposition as defined in claim 2 further including the addition of anamount of flocculent to achieve a desired viscosity.
 14. The compositionas defined in claim 12 further including the addition of an amount ofdeflocculent to achieve a desired viscosity.
 15. An improved method forforming an electrically conductive glaze upon a ceramic mold formcomprising:(a) forming a combination comprising feldspar (30.0-35.0percent by weight), flint (18.0-22.0 percent by weight), calciumcarbonate (7.0-11.0 percent by weight), ball clay (1.0-2.0 percent byweight), kaolin (2.0-4.2 percent by weight), zinc oxide (5.0-10.0percent by weight), black iron oxide (25.0-30.0 percent by weight); (b)forming a solution by mixing five parts by weight of said combinationwith from three to five parts water by weight; (c) adjusting theviscosity of the solution as desired by adding an amount of flocculentor deflocculent thereto; (d) applying the solution to the surface of aceramic mold form; and (e) heating the coated ceramic mold form to forman electrically conductive glaze thereon.
 16. The method as defined inclaim 15 wherein said mixing is performed with sufficient water to yielda resulting solution having a specific gravity of from 1.52-1.62. 17.The method as defined in claim 15 wherein the heating is performed bythe temperature of approximately 2,260 degrees Fahrenheit for a cycle ofapproximately 30 hours.
 18. The method as defined in claim 15 whereinthe applying of the solution is performed by dipping of the ceramic moldform therein.
 19. The method as defined in claim 15 wherein the applyingof the solution is performed by spraying of the ceramic mold formtherein.
 20. The method as defined in claim 15 further includingscreening of the solution through a #150 mesh filter after adjusting thespecific gravity and prior to the adjusting of the viscosity by addingof the 20 percent magnesium sulphate solution.